Chapter 5 5-4 Using sum and difference formulas

Objectives

Use sum and difference formulas to evaluate trigonometric identities

Verify trigonometric identities

Using sum and difference formulas

Sum and Difference Formulas:

Example #1 evaluating trigonometric functions

Find the exact value of

A) cos 75

B)

C) sin(15o

EXAMPLE

What’s the exact value of tan 15° or tan(π/12)? 

EXAMPLE#2 EVALUATING TRIGONOMETRIC FORMULAS

Given sin x = 1 / 5 and sin y = -2 / 3, angle x is in quadrant II and angle y is in quadrant III, find the exact value of sin(x + y).

EXAMPLE

find the exact value of the trigonometric function given that

sinu =5 /13 and cosv = −3/ 5(Both u and v are in Quadrant II).

Proving a cofunction Identity

Prove the cofunction identity = sin x.

Example

Verify that

Example

Simplify

Worksheet

Let do the following worksheet as a project